The present invention relates to a cassette containing a sheet- or strip-like medium and, more particularly, to a cassette with a mechanism for preventing the slackening of the sheet- or film-like medium.
There have been long used cassettes of the type in which two reels are rotatably mounted in parallel with each other in the cassette case so that a sheet- or strip-like medium is unwound from one reel and then wound around the other reel. In the case of such cassettes of the type described above, it is preferable to provide a mechanism for preventing the rotation of reels in order to prevent the slackening of the wound medium when the cassettes are not used. For instance, such mechanism is disclosed in Japanese Laid-Open Patent Application (Kokai) No. Sho-61-152,475. In this mechanism, springs are mounted within the cassette case such that they normally bias the reel only in one axial direction thereof so as to engage a projection extended from one end face of each reel with an engaging recess formed in the side wall of the cassette case in opposed relationship with the projection, thereby preventing the rotation of the reel.
However, in this cassette, one side wall of the cassette case must be formed with an engaging recess or projection for engagement with an engaging projection or recess of the reel so that there arises the problem that the fabrication costs of the cassettes increase.
The present invention was made to substantially solve the above and other problems encountered in the conventional cassettes and has for its object to provide a cassette capable of preventing the rotation of reels without forming one or more projections or recesses for preventing the rotation of the reels in the cassette case itself.
To the above and other ends, according to the present invention, in a cassette of the type in which reels carrying a sheet-like medium wound there around are rotatably mounted in a cassette case in such a manner that the reels are movable in their longitudinal directions, a winding slack preventing mechanism is provided which comprises: rotation preventing means extending axially outwardly of one end of at least one of the reels; a projection on said rotation preventing means, extending axially outwardly; said rotation preventing means and said projection being disposed within a space defined in said cassette case; and a reel-biasing leaf-spring assembly provided in said space to bias the reel longitudinally thereof in a direction opposite to the direction in which said projection projects, said leaf-spring assembly being in contact with said projection for biasing the reel and having on the distal end thereof a rotation preventing arm disposed adjacent to, and normally engaging said rotation preventing means to prevent the rotation of the reel, said leaf-spring assembly being so designed and constructed that when the reel is pushed in the direction opposite to the direction in which said leaf-spring assembly imparts the biasing force so that said leaf-spring assembly is deformed, said rotation preventing arm is moved away from said rotation preventing means, thereby to allow the reel to rotate.